U.S. Pat. No. 6,340,067 discloses a bicycle equipped with a drive assist, i.e., a motor assist bicycle. When a pedaling force detected by a pedaling force sensor exceeds a reference value, the drive assist is actuated to reduce a loading of a driver. The bicycle includes a drive assist attached to a driving wheel, a driving power transmission means attached between a sprocket and a rear wheel, a pair of pedal levers, a crank lever for transmitting a rotation force of the pedal lever to the sprocket, and a sliding portion serving as a swing fulcrum of the pedal lever. The pedaling force sensor is attached to a part of the pedal lever which makes nearly reciprocating motion, and the output from the sensor is supplied through a single wire or the like to a controller which controls the drive assist.
U.S. patent application publication no. 2014/0200835 discloses a pedaling torque sensor device for bicycles in which strain gauges are non-detachably fixed on an inside of a crank arm.
U.S. Pat. No. 8,881,608 discloses a bicycle crank arm including a crank body, a sensor support member, and a power sensing device. The crank body includes a crank axle mounting portion and a pedal mounting portion. The sensor support member is disposed in a cavity of the crank body and attached to the crank body. The power sensing device is supported on the sensor support member.